I just implemented the FreeTrack protocol in an Unreal Engine 4 plugin. I'd like to share this back with the community (and use it in my own dev efforts!) but I'm a bit confused by the licensing status of FreeTrack client implementations.

Since FreeTrack is GPL-licensed, and any shared memory client by definition runs afoul of the GPL (reference the GPL faq), does this mean I can not distribute my plugin under anything but the GPL?

It looks like Bohemia Interactive Studios (Arma / etc) have been shipping FreeTrack-compatible versions of their games for a while now, and the community has written FreeTrack drivers for a host of closed-source games.